magneto

Fri Mar 01, 2013 10:36 pm

I recently purchased two 1948 cubs, one manual and one hydraulic. They came as a package deal. The manual has been sitting for years and is a parts tractor although it is all there and should be restorable. The other is in the garage and was a runner last year. I have two magnetos, neither of which worked. I found a broken wire from the coil to the post, repaired it and it sparks great. After some carb issues, the tractor started right up and ran great. I hooked up the kill switch as it was when I got it, to the magneto post. While test driving the tractor, I used the kill switch to stop the engine. It worked but wires started smoking behind the dash. I unhooked the battery to stop the meltdown. I also unhooked the kill switch from the mag post. The tractor no longer runs and the mag no longer produces a spark.

What happened here?

Re: magneto

Fri Mar 01, 2013 10:51 pm

it sounds like the coil is fried. Did this tractor originally have[a mag. Sure sounds like a short in the wiring that caused the smoke.

Re: magneto

Fri Mar 01, 2013 11:02 pm

Both tractors came with magnetos. Is there a way to test the coil with an ohm meter? From everything I have seen, the magneto is independent of all the wiring with the exception of the kill switch and that connection is just supposed to ground out the magneto. I believe due to an incorrect connection, power went into the magneto the wrong way. I am not good at electrical but the only things I see inside the magneto is the condenser, the points and the coil. Could I have ruined the coil or could the condenser be damaged?

Re: magneto

Fri Mar 01, 2013 11:05 pm

First off, G'day and congrats on acquiring your very 1st new to you Cub and joining the MCC at the same time

We have a number of members here who are super at electrics and mags. They will be along to help shortly. And I see one of the masters has already replied... What I can do is what I do best and that is the Welcome Wagon and pointing to our resources of which there are legion.

Below is a wiring schematic for a magneto equipped Cub with Generator, Cut-out, Lights, Starter and a Battery.

As you can see in the parts breakdown above, the coil is contained inside the square cover.

Re: magneto

Sat Mar 02, 2013 7:34 am

when you push the switch in on a mag it puts a ground in the circuit shutting the spark down from it. I think that there is a short in the wiring between the wire going to the mag and a wire carrying voltage. Find the short before going much further. I have never been able to check the coil with a volt meter. You can however use an external coil. A mag coil can be found on ebay for about 60 dollars.

Re: magneto

Sat Mar 02, 2013 7:43 am

Obviously, you'll need to check out the wiring to see what the smoking was all about, but if it has been miswired and voltage was applied to the mag kill stud it may have overheated the return spring on your points. That's a dead short in this case. I encountered that twice in one day! At first, I couldn't figure out what could do that to the points. I replaced the points and handed the mag back to the owner. He installed it and when checked it had no spark, again. When I pulled it back apart and found the same problem again, I went out to the tractor for a look. Sure enough, it had been wired for an external coil. I told him not to hook up the kill wire, it started right up this time. I don't think your coil would be damaged from this.

Re: magneto

Sat Mar 02, 2013 8:19 am

Someone could have put the wrong kill switch on it. You need a single wire switch.

Re: magneto

Sat Mar 02, 2013 10:35 am

Was checking my searches and came across an original '48 Owner's Manual

If you find voltage in one of the switch positions - wrong switch for magneto and tractor wired for battery powered ignition system.

Agree with Gary, most likely a short caused the magneto points to fault.

Re: magneto

Sat Mar 02, 2013 3:22 pm

Thanks to everyone for help on this issue. It was indeed the points spring as mentioned by Gary Dotson. Once I fixed that problem, the tractor started right up. I will continue to work on the electrical wiring for the lights, ameter and generator. The schematic is very useful although my tractor is negative ground, not positive. I still have one dead magneto that belongs to my other tractor. I will keep at it.

I have been struggling with this issue for 2 weeks taking stabs in the dark.. Thanks to this great resource and the help of people who know about cubs, I was successful. Thanks again for the help. We will talk some more.

Re: magneto

Sun Mar 03, 2013 8:43 am

I'm glad I was able to help you on this! It seems kinda odd that it will kill the spring, rather than frying the contacts, but that's what it seems to do.

Re: magneto

Thu Mar 07, 2013 11:21 pm

One magneto was still not working. To test the coil, I put in the coil from the working magneto into the one that did not work. To my surprise, it worked. So it was a bad coil in the second magneto that kept it from working. I purchased a new coil on e-bay and received it yesterday. It has now been installed and the magneto ready for installation. I will perform the final test this weekend to see if I can get my second cub to run. The carb has been rebuilt and new plug wires are ready to go. I am hopeful that this cub that has been sitting in a field for years will come back to life.

Re: magneto

Fri Mar 08, 2013 2:55 am

WELCOME CUB-OREGON

YOU CAN GET A MOMENTARY TOGGLE SWITCH AT A AUTO-PARTS STORE FOR 2 (+/-) BUCKS AND THAT WILL WORK FOR THE KILL SWITCH----- ( GROUND ONE SIDE AND MAG. WIRE ON OTHER SIDE )---- NO HOT WIRES------